This invention concerns improvements in or relating to ablutionary installations for washing such as baths, showers, washbasins and the like.
The invention has particular, but not exclusive application to single or multiple outlet installations such as may be employed both domestically in the home and commercially in a variety of situations including hotels, healthcare and leisure establishments.
Typical installations for showering in healthcare and leisure establishments employ thermostatic mixing valves for mixing and blending supplies of hot and cold water to provide a source of temperature controlled water. Such installations carry risks associated with the safe operation of the mixing valve to avoid the user being scalded by discharge of very hot water and with the reliable disinfection of the waterways to prevent the user being infected by the presence of bacteria in the water supply, especially legionella bacteria.
Accurate control of the outlet water temperature is therefore required in such installations to reduce the risk of scalding. Electronic thermostatic mixing valves are known that employ a control system including a temperature sensor to monitor the outlet water temperature and an electric motor to adjust the position of the proportioning valve to maintain the selected water temperature substantially constant.
These valves can provide a fast response to change in temperature of the outlet water but the known electronic thermostatic mixing valves can tend to instability where the pressures of the hot and cold water supplies are unequal. Various attempts have been made to improve stability while maintaining accurate temperature control.
One method used to keep an electronic thermostatic mixing valve stable is to build in a level of damping in the valve rate of correction. This has the disadvantage that the valve becomes sluggish in response and so a compromise has to be selected wherein the accuracy of control and damping are satisfactory for a specific set of operating conditions, including the specification of the shower spray to be used.
Another method is to provide a motorised addition to the control knob of a thermostatic mixing valve employing a thermostat containing a thermally responsive material where the filled thermostat deals with adverse inlet pressure changes whilst remaining stable and the electronic addition makes very small, damped adjustments to the mixing valve temperature selector knob to compensate for the small residual errors. The component count in this type of valve is quite high because there is a complete mechanical control system plus an electronic control system so the product cost is consequently moderately high.
A potential solution to these problems involves employing sensors for the pressure, temperature and flow rate of the hot and cold water at the inlets and the blended water at the outlet and to adjust the ratio of hot and cold water delivered to the outlet in response to change in any of these affecting the outlet water temperature. The provision of sensors for all these parameters adds considerably to manufacturing costs and adds to the complexity of the electronic control required to process the signals and generate a correction signal.
It is common practice for a trained technician to carry out tests on each mixing valve in an installation when it is commissioned and then at regular intervals to ensure that the mixing valves are working properly. This is highly labour intensive and carrying and recording the tests manually incurs significant costs. Moreover, while regular testing may enable a gradual deterioration in the performance of a mixing valve to be detected and rectified before a serious fault develops, such routine testing cannot eliminate the risks of scalding resulting from a catastrophic failure of a mixing valve between tests.
It is also common practice for the installation to be constructed from pipes and fittings that are made from materials approved for use in potable water supply systems with the hot water system maintained at a temperature above 60 degrees C. to kill any organisms and the cold water system kept below 20 degrees C. to prevent any organisms that are present from growing quickly. In this way, the risk of bacteria such as legionella surviving and breeding in the installation is considerably reduced. Problems can still arise, however, if any part of the system is not used for any length of time where water can stagnate in the pipe work allowing any bacteria that are present to grow. As a result, it is necessary to flush the system to prevent water stagnating in the pipe work. This currently requires a service engineer to manually open and close the outlets to flush the water from the pipe work. This is highly labour intensive and there is a risk that parts of the system may not be flushed if any of the outlets are missed which can result in harmful bacteria growing to produce a health risk when the outlet is next opened.
In addition, the installation may be disinfected at pre-determined intervals by flushing with water heated above 60° C. for a minimum time sufficient to kill any bacteria present in the waterways. Such elevated water temperatures would produce scalding and requires disinfection to be carried out in a controlled manner when no-one is present in the shower area where they could be exposed to the hot water.
Thermostatic mixing valves for mixing and blending supplies of hot and cold water to provide a source of temperature controlled water are also widely used for showering in domestic and commercial establishments such as hotels. In these installations, the user typically steps into a shower enclosure to operate the mixing valve. When the shower has not been used for some time, a dead leg of cold water between the mixing valve and the shower head is discharged on starting the shower so that the user experiences an initial shot of cold water that may last for several seconds until the water having the selected temperature is delivered to the shower outlet. This can be uncomfortable and may cause the user to adjust the mixing valve to increase the selected water temperature. This may result in water being discharged that is too hot. Although this may not be dangerous for many users, it is uncomfortable and, in the case of young children or the elderly, could cause scalding. This can be a particular problem when young children or the elderly are allowed to shower unsupervised. Often, they are unfamiliar with the operations of the controls and this may lead to inadvertent selection of water that is too hot.
Many users also like to stop the shower while applying soap or shampoo. As a result, the temperature setting of the mixing valve is lost when the valve is turned off and, when the valve is turned on again, the user experiences an initial shot of cooler water until the valve discharges water having the selected temperature. This is uncomfortable and requires the user to remember the valve position to return the shower to the original setting.